1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine or a printer of the electrophotographic type.
2. Description of Related Art
Electrophotographic-type image forming apparatuses using powdered developing agents (toners) are employed as the output apparatuses of computers or workstations. The image forming apparatus of this type is provided with a photosensitive drum for forming thereon an electrostatic latent image while the photosensitive drum is rotating, a developing device for supplying the developing agent to the electrostatic latent image formed on the photosensitive drum, and an image forming part for forming an image on a recording medium by transferring the developed image to the recording medium. The image forming apparatus generally further includes a paper feeding part arranged to send the recording medium (paper) to the image forming part, and a delivery part disposed on one side opposite to the paper feeding part across the image forming part. A recording medium transport path is thus formed to transport the recording medium from the paper feeding part toward the delivery part.
Generally, the recording medium transport path laterally extends as viewed from the front side of the image forming apparatus. The axis of a rotating shaft of the photosensitive drum extends almost perpendicularly to the recording medium transport path. Further, the developing device is provided with a developing roller for supplying the photosensitive drum with the developing agent. The developing agent is supplied to the photosensitive drum while the developing roller is rotating. The rotating shaft of the developing roller is arranged to extend approximately in parallel with the rotating shaft of the photosensitive drum. With these rotating shafts arranged to be approximately in parallel with each other, a uniform amount of the developing agent is supplied from the developing roller to the photosensitive drum.
Some of such image forming apparatuses are of a so-called clamshell type. The clamshell-type image forming apparatus has a turning shaft which is disposed at one end part thereof in the direction of orthogonally intersecting the recording medium transport path (a rear side part), and an opening-and-closing part which is disposed at the other end part (a front side part), in the orthogonally intersecting direction, opposite to the turning shaft. Thus, the body of the clamshell-type image forming apparatus is arranged to be able to be divided into an upper structural body and a lower structural body by opening and closing the opening-and-closing part. In the case of the clamshell-type image forming apparatus, the recording medium transport path can be exposed to a great degree by opening the opening-and-closing part. This facilitates trouble shooting work by the user in the event of, for example, jamming of paper.
In the clamshell-type electrophotographic image forming apparatus, it is general that the photosensitive drum and the developing device are disposed within the upper structural body and the cassette tray and the fixing device are disposed within the lower structural body. While the lower structural body is fixed, a front part of the upper structural body is arranged to be pushed upward by means of a damper which has air or the like sealed therein.
With the photosensitive drum and the developing device disposed inside the upper structural body of the clamshell-type image forming apparatus, when the upper structural body is turned upward, the photosensitive drum and the developing device slant accordingly. In this instance, the developing agent contained in the developing device tends to move downward to gather on one side accordingly as the developing device slants. The one-sided gathering of the developing agent tends to cause the amount of the developing agent, which is supplied from the developing roller to the photosensitive drum, to be supplied unevenly in the axial direction of the rotating shaft of the developing roller. Such an uneven supply of the developing agent causes the developed image on the drum to have uneven density and thus eventually lowers the quality of an image formed on the recording medium.